IGPP is pleased to invite you to join its Winter 2024 Seminar Series presentation featuring University of Illinois Urbana Champaign's Ahmed Elbanna. Dr. Elbanna's talk, "The Earthquake Virtual Machine: Modeling Fault Zone Seismogenesis Through Space and Time" will occur at 3pm WEDNESDAY May 22, 2024.
Time: 3:00 pm, Pacific Time
Location: Revelle Conference Room
Abstract: While significant progress has been made in understanding earthquake source processes in linear elastic domains, the effect of more realistic inelastic rheologies including plasticity is poorly understood. Here, we simulate the co-evolution of shear fractures on pre-existing fault surfaces and bulk inelastic deformation through modeling a sequence of (fast) earthquakes and (slow) aseismic slip of a 2D rate-and-state frictional interface embedded in a full-space elastic-plastic bulk. We use a hybrid finite element spectral boundary integral (FEBE) scheme that relies on domain decomposition in space and extreme adaptive stepping in time. The hybrid computational scheme enables exact near-field truncation of the elastodynamic field allowing us to use high resolution finite element discretization in a narrow region surrounding the fault zone that encompasses the potential plastic deformation. Wave propagation and long range static stress transfer in the exterior half spaces are handled using the spectral boundary integral equation. The adaptive time stepping is based on the maximum velocity jump across the fault surface. The resulting time step varies from milliseconds to days enabling the simulation of both slow deformation and fast dynamic ruptures over multiple earthquake cycles.
Our study reveals that off-fault plasticity can cause both partial ruptures and temporally clustered seismic activities. The interplay between fault slip and off-fault plasticity leads to areas with reduced fault slip, indicating that some permanent deformation happens throughout the material as inelastic strain. This contrasts with an entirely elastic scenario, where all inelastic deformation is confined to the fault surface. If the yield stress is high relative to the fault’s frictional strength, the plastic deformation dissipates only a few percent of the total energy budget. Nonetheless the impact of plasticity in this case on the seismic cycle can still be significant through its effect on stress distribution and viscous relaxation. Conversely, if the bulk's yield stress is low enough to be comparable to the fault's frictional strength, new rupture patterns emerge. These are marked by extensive energy dissipation within the bulk and slow or creeping ruptures on the fault without much noticeable inertia effects. Considering a Weibull distribution of yield strength, the long-term seismic pattern turns out to be governed by the average yield strength rather than its spatial variability. We also show how plasticity controls fault zone evolution through a series of additional examples including fault step overs and fracture corridors. Our findings highlight the pivotal role of bulk strength in earthquake dynamics across different scales and propose a novel aspect of dynamic variability in earthquake physics, potentially influencing fault zone morphogenesis as well as earthquake size and energy distribution.
Bio: Ahmed E. Elbanna holds a Ph.D. in civil engineering and an M.S. in applied mechanics both from CALTECH, and an M.S. in structural engineering and B.S. in civil engineering from Cairo University. He has been on the faculty at UIUC since 2013 and he currently leads the Mechanics of Complex Systems Laboratory. He is a Donald Biggar Willett Faculty Fellow at the Grainger College of Engineering and Associate Professor of Structural Engineering and Mechanics in the Civil Engineering Department. Dr. Elbanna's research on problems in theoretical and applied mechanics of solids, in the presence and absence of pore fluids, with special emphasis on fracture, deformation and wave propagation problems as they arise in geophysics, soft materials, and material design. He is a fellow of NCSA, a faculty affiliate of Beckman Institute of Advanced Studies, a recipient of NSF Faculty Early CAREER award, and the recipient of the 2019 Journal of Applied Mechanics Paper Award. He currently serves as a co-leader of the Computational Science thrust of the Statewide California Earthquake Center.